Various types of craft or vehicles are dropped or propelled into contact with a landing surface with sufficient force to require energy absorbing devices for cushioning the landing impact. For example, spacecraft landings, cargo dropped containers and the like have utilized energy absorbing systems such as parachutes to slow landing velocities, air bag systems, skidding devices, retro-rocket firing to decrease velocity, unidirectional crushable honeycomb devices, frangible tube devices and hydraulic pneumatic shock absorbers.
Where the landing is on a surface without atmosphere, parachute systems or air-drag dependent systems are of little value. Air bags require a compressed air container and a system of valves which are subject to mechanical malfunctions. Moreover, with this type of device, it is difficult to control the landing with any predictability and stability of the vehicle can be a problem.
Some landing devices contemplate skidding along the surface when landing and use of spikes for dragging the surface. This type of device offers only unidirectional energy absorption, and can dissipate either horizontal or vertical velocity, but not both. The two methods may not be used in conjunction with each other, so another system must also be used to dissipate the uncontrolled energy. These systems also rely heavily on the properties of the landing surface being utilized. Since it is often difficult to pinpoint exactly where the vehicle will land and the surface properties at the final landing site, these systems are not very desirable.
Retro-rocket firing from the vehicle is an effective method for cushioning landing forces, but it requires a complicated rocket device and fuel which, as a system, is very heavy and difficult to maintain. Near the landing surface, plume impingement from the rockets can also create problems.
Other devices, such as unidirectional honeycomb device in a landing pad, offer effective methods, of energy absorption, but unidirectional honeycomb can only absorb energy in one direction. Frangible tubes rely on material deformation to absorb energy, but provide very unpredictable and varying degrees of energy absorption.
Hydraulic and pneumatic shock absorbers are also effective for energy absorption, but are very difficult to maintain in working order in the unique environment of space. In addition, sealing problems in shock absorbers are very common in space related activities. The shock absorbers also tend to be complicated and heavier than many of the other methods or devices described or presented in this document.
Another important disadvantage of many of the above methods or devices is that the mechanisms which perform these functions must be located within the structure of the vehicle. This means that much of the landing load imported into parts of the structure of the vehicle cannot be limited. For example, all the landing structure located below shock or energy absorbers must be large enough to survive a very high impact load. In addition, the impact loading on the landing structure is highly dependent on landing velocities, landing surface conditions, structural weights, and many factors which are difficult to quantify early in a program and present problems which are difficult to change or modify later.
The landing system which is the subject of this invention absorbs the energy with a constant load (force) for a wide range of velocities, surfaces, weights, etc.